{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,9,1]],"date-time":"2026-09-01T13:23:29Z","timestamp":1788269009695,"version":"build-2803163510"},"reference-count":40,"publisher":"MDPI AG","issue":"5","license":[{"start":{"date-parts":[[2026,8,26]],"date-time":"2026-08-26T00:00:00Z","timestamp":1787702400000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"Belgian Ministry of Social Affairs"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Infect. Dis. Rep.","Infectious Disease Reports"],"abstract":"<jats:p>Background: Legionnaires\u2019 disease (LD) is most often described as caused by a single Legionella pneumophila (Lp) serogroup (SG), typically SG1. However, mixed infections involving multiple SGs or even different Legionella species can occur within a single host. Such cases remain underrecognized and pose challenges for diagnosis, clinical management, and outbreak investigation. Case presentation: A 61-year-old woman developed acute fever, malaise, and productive cough after visiting a wellness spa in France, with radiological findings consistent with a lower respiratory tract infection. The urinary antigen test (UAT) for Lp was negative, but respiratory multiplex PCR was weakly positive. Subsequent testing at the Belgian National Reference Centre (NRC) for Legionella revealed an unexpected discordance between an in-house SG1-specific PCR and culture-based findings. Further analysis identified co-infection with two distinct Lp strains, SG1 (sequence type, ST146) and SG10 (ST1267), using a combination of direct sequence-based typing (SBT) and culture with serogrouping of multiple colonies. The patient improved rapidly after treatment with oral levofloxacin. Conclusions: Mixed Lp SG infections are likely underrecognized in routine practice, as neither UAT, commercial molecular assays, nor characterization of a single cultured isolate may adequately capture within-host strain diversity. Comprehensive diagnostic approaches combining culture with analysis of multiple colonies and molecular tests are essential for accurate case detection and source attribution. Referral to NRCs is recommended when advanced typing methods are unavailable. This first reported Belgian case illustrates the potential implications for patient management and epidemiological investigations, underscoring the need for broader diagnostic strategies.<\/jats:p>","DOI":"10.3390\/idr18050093","type":"journal-article","created":{"date-parts":[[2026,8,26]],"date-time":"2026-08-26T15:04:32Z","timestamp":1787756672000},"page":"93","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["Mixed Legionella pneumophila Serogroup Infection in a Single Patient: Case Report and Literature Review"],"prefix":"10.3390","volume":"18","author":[{"ORCID":"https:\/\/orcid.org\/0009-0001-4970-0222","authenticated-orcid":false,"given":"Bram","family":"Vanmechelen","sequence":"first","affiliation":[{"name":"Department of Microbiology, Universitair Ziekenhuis Brussel (UZ Brussel), Vrije Universiteit Brussel (VUB), 1090 Brussels, Belgium"},{"name":"Vitality Research Group, Vrije Universiteit Brussel (VUB), 1090 Brussels, Belgium"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-8075-1012","authenticated-orcid":false,"given":"Fedoua","family":"Echahidi","sequence":"additional","affiliation":[{"name":"Department of Microbiology, Universitair Ziekenhuis Brussel (UZ Brussel), Vrije Universiteit Brussel (VUB), 1090 Brussels, Belgium"},{"name":"Vitality Research Group, Vrije Universiteit Brussel (VUB), 1090 Brussels, Belgium"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-6465-3666","authenticated-orcid":false,"given":"Stijn","family":"Jonckheere","sequence":"additional","affiliation":[{"name":"Department of Laboratory Medicine, Jan Yperman Hospital, 8900 Ypres, Belgium"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0009-0006-3313-9377","authenticated-orcid":false,"given":"Patricia","family":"Vandecandelaere","sequence":"additional","affiliation":[{"name":"Department of Laboratory Medicine, Jan Yperman Hospital, 8900 Ypres, Belgium"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Ines","family":"Malysse","sequence":"additional","affiliation":[{"name":"Department of Internal Medicine, Jan Yperman Hospital, 8900 Ypres, Belgium"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-4281-9749","authenticated-orcid":false,"given":"Oriane","family":"Soetens","sequence":"additional","affiliation":[{"name":"Department of Microbiology, Universitair Ziekenhuis Brussel (UZ Brussel), Vrije Universiteit Brussel (VUB), 1090 Brussels, Belgium"},{"name":"Vitality Research Group, Vrije Universiteit Brussel (VUB), 1090 Brussels, Belgium"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-0250-2664","authenticated-orcid":false,"given":"Charlotte","family":"Michel","sequence":"additional","affiliation":[{"name":"Department of Microbiology, Universitair Ziekenhuis Brussel (UZ Brussel), Vrije Universiteit Brussel (VUB), 1090 Brussels, Belgium"},{"name":"Vitality Research Group, Vrije Universiteit Brussel (VUB), 1090 Brussels, Belgium"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2026,8,26]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"279","DOI":"10.1007\/s00005-009-0035-8","article-title":"Pathogenicity of the family Legionellaceae","volume":"57","year":"2009","journal-title":"Arch. Immunol. Ther. Exp."},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"729","DOI":"10.1007\/s10096-019-03785-8","article-title":"What is the risk of missing legionellosis relying on urinary antigen testing solely? A retrospective Belgian multicenter study","volume":"39","author":"Muyldermans","year":"2020","journal-title":"Eur. J. Clin. Microbiol. Infect. Dis."},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"973","DOI":"10.1007\/s40121-022-00635-7","article-title":"Legionnaires\u2019 Disease: Update on Diagnosis and Treatment","volume":"11","author":"Viasus","year":"2022","journal-title":"Infect. Dis. Ther."},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"O13","DOI":"10.1111\/1469-0691.12311","article-title":"Dual infections with different Legionella strains","volume":"20","author":"Wewalka","year":"2014","journal-title":"Clin. Microbiol. Infect."},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"307","DOI":"10.1016\/j.ijmm.2013.11.002","article-title":"Mixed infection by Legionella pneumophila in outbreak patients","volume":"304","author":"Coscolla","year":"2014","journal-title":"Int. J. Med. Microbiol."},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"1242","DOI":"10.1099\/jmm.0.016089-0","article-title":"Isolation of Legionella rubrilucens from a pneumonia patient co-infected with Legionella pneumophila","volume":"59","author":"Matsui","year":"2010","journal-title":"J. Med. Microbiol."},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"242","DOI":"10.1007\/s15010-004-2127-z","article-title":"Mixed lung infection by Legionella pneumophila and Legionella gormanii detected by fluorescent in situ hybridization","volume":"32","author":"Buchbinder","year":"2004","journal-title":"Infection"},{"key":"ref_8","doi-asserted-by":"crossref","unstructured":"Papadakis, A., Koufakis, E., Chaidoutis, E.A., Chochlakis, D., and Psaroulaki, A. (2025). Comparative Risk Assessment of Legionella spp. Colonization in Water Distribution Systems Across Hotels, Passenger Ships, and Healthcare Facilities During the COVID-19 Era. Water, 17.","DOI":"10.20944\/preprints202506.0986.v1"},{"key":"ref_9","doi-asserted-by":"crossref","unstructured":"Marras, L., Bertolino, G., Sanna, A., Carraro, V., and Coroneo, V. (2023). Legionella spp. Monitoring in the Water Supply Systems of Accommodation Facilities in Sardinia, Italy: A Two-Year Retrospective Analysis. Int. J. Environ. Res. Public Health, 20.","DOI":"10.3390\/ijerph20186722"},{"key":"ref_10","doi-asserted-by":"crossref","unstructured":"Barigelli, S., Koper, P., Petricciuolo, M., Firrincieli, A., Palusinska-Szysz, M., and Federici, E. (2025). Unravelling the Genomic and Virulence Diversity of Legionella pneumophila Strains Isolated from Anthropogenic Water Systems. Microorganisms, 13.","DOI":"10.3390\/microorganisms13122832"},{"key":"ref_11","doi-asserted-by":"crossref","unstructured":"Buse, H.Y., Morris, B.J., Gomez-Alvarez, V., Szabo, J.G., and Hall, J.S. (2020). Legionella Diversity and Spatiotemporal Variation in The Occurrence of Opportunistic Pathogens within a Large Building Water System. Pathogens, 9.","DOI":"10.3390\/pathogens9070567"},{"key":"ref_12","doi-asserted-by":"crossref","unstructured":"Qin, T., Yan, G., Ren, H., Zhou, H., Wang, H., Xu, Y., Zhao, M., Guan, H., Li, M., and Shao, Z. (2013). High prevalence, genetic diversity and intracellular growth ability of Legionella in hot spring environments. PLoS ONE, 8.","DOI":"10.1371\/journal.pone.0059018"},{"key":"ref_13","unstructured":"European Centre for Disease Prevention and Control (2026). Legionnaires\u2019 Disease\u2014Annual Epidemiological Report for 2023, European Centre for Disease Prevention and Control."},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"e01487","DOI":"10.1016\/j.idcr.2022.e01487","article-title":"Non-Legionella pneumophila serogroup 1 pneumonia: Diagnosis of a nosocomial legionellosis with the Biofire Pneumonia plus panel","volume":"28","author":"Courboules","year":"2022","journal-title":"IDCases"},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"1387","DOI":"10.1007\/s10096-015-2363-4","article-title":"Design and validation of a qPCR assay for accurate detection and initial serogrouping of Legionella pneumophila in clinical specimens by the ESCMID Study Group for Legionella Infections (ESGLI)","volume":"34","author":"Mentasti","year":"2015","journal-title":"Eur. J. Clin. Microbiol. Infect. Dis."},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"295","DOI":"10.1016\/j.diagmicrobio.2016.03.022","article-title":"Simultaneous detection of Legionella species and L. anisa, L. bozemanii, L. longbeachae and L. micdadei using conserved primers and multiple probes in a multiplex real-time PCR assay","volume":"85","author":"Cross","year":"2016","journal-title":"Diagn. Microbiol. Infect. Dis."},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"576","DOI":"10.1128\/JCM.41.2.576-580.2003","article-title":"Diagnosing herpesvirus infections by real-time amplification and rapid culture","volume":"41","author":"Guldemeester","year":"2003","journal-title":"J. Clin. Microbiol."},{"key":"ref_18","doi-asserted-by":"crossref","first-page":"2047","DOI":"10.1128\/JCM.43.5.2047-2052.2005","article-title":"Consensus sequence-based scheme for epidemiological typing of clinical and environmental isolates of Legionella pneumophila","volume":"43","author":"Gaia","year":"2005","journal-title":"J. Clin. Microbiol."},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"1965","DOI":"10.1128\/JCM.00261-07","article-title":"Addition of neuA, the gene encoding N-acylneuraminate cytidylyl transferase, increases the discriminatory ability of the consensus sequence-based scheme for typing Legionella pneumophila serogroup 1 strains","volume":"45","author":"Ratzow","year":"2007","journal-title":"J. Clin. Microbiol."},{"key":"ref_20","unstructured":"(2025, April 24). El Gato Pipeline. Available online: https:\/\/github.com\/appliedbinf\/el_gato."},{"key":"ref_21","unstructured":"(2025, April 24). MOST Pipeline. Available online: https:\/\/github.com\/phe-bioinformatics\/MOST."},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"449","DOI":"10.1038\/s41598-023-27723-z","article-title":"Genotypic resistance determined by whole genome sequencing versus phenotypic resistance in 234 Escherichia coli isolates","volume":"13","author":"Vanstokstraeten","year":"2023","journal-title":"Sci. Rep."},{"key":"ref_23","doi-asserted-by":"crossref","first-page":"981","DOI":"10.1128\/JCM.02071-08","article-title":"Evaluation of a nested-PCR-derived sequence-based typing method applied directly to respiratory samples from patients with Legionnaires\u2019 disease","volume":"47","author":"Ginevra","year":"2009","journal-title":"J. Clin. Microbiol."},{"key":"ref_24","unstructured":"(2025, April 16). Legionella Species Identification by Mip Similarity. Available online: http:\/\/www.hpa-bioinformatics.org.uk\/cgi-bin\/legionella\/mip\/mip_id.cgi."},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"119","DOI":"10.1007\/978-1-62703-161-5_6","article-title":"Typing methods for Legionella","volume":"954","author":"Luck","year":"2013","journal-title":"Methods Mol. Biol."},{"key":"ref_26","doi-asserted-by":"crossref","first-page":"240","DOI":"10.7326\/0003-4819-93-2-240","article-title":"Legionnaires\u2019 disease: Unusual clinical and laboratory features","volume":"93","author":"Meyer","year":"1980","journal-title":"Ann. Intern. Med."},{"key":"ref_27","doi-asserted-by":"crossref","first-page":"1106","DOI":"10.1128\/jcm.26.6.1106-1110.1988","article-title":"Simultaneous infections with different serogroups of Legionella pneumophila investigated by routine methods and Fourier transform infrared spectroscopy","volume":"26","author":"Horbach","year":"1988","journal-title":"J. Clin. Microbiol."},{"key":"ref_28","doi-asserted-by":"crossref","first-page":"367","DOI":"10.3109\/00365549009027062","article-title":"Nosocomial infection with Legionella pneumophila serogroup 1 and 8 in a neonate","volume":"22","author":"Aubert","year":"1990","journal-title":"Scand. J. Infect. Dis."},{"key":"ref_29","doi-asserted-by":"crossref","first-page":"277","DOI":"10.5694\/j.1326-5377.1997.tb140117.x","article-title":"Legionnaires\u2019 disease: Co-infection with Legionella pneumophila serogroups 1 and 5","volume":"166","author":"Jalaludin","year":"1997","journal-title":"Med. J. Aust."},{"key":"ref_30","doi-asserted-by":"crossref","first-page":"1160","DOI":"10.1128\/JCM.36.4.1160-1163.1998","article-title":"Nosocomial pneumonia caused by three genetically different strains of Legionella pneumophila and detection of these strains in the hospital water supply","volume":"36","author":"Luck","year":"1998","journal-title":"J. Clin. Microbiol."},{"key":"ref_31","doi-asserted-by":"crossref","first-page":"48","DOI":"10.1093\/cid\/cit176","article-title":"First outbreak of nosocomial Legionella infection in term neonates caused by a cold mist ultrasonic humidifier","volume":"57","author":"Yiallouros","year":"2013","journal-title":"Clin. Infect. Dis."},{"key":"ref_32","doi-asserted-by":"crossref","first-page":"1242","DOI":"10.3201\/eid2007.131343","article-title":"Legionnaires\u2019 disease caused by Legionella pneumophila serogroups 5 and 10, China","volume":"20","author":"Zhang","year":"2014","journal-title":"Emerg. Infect. Dis."},{"key":"ref_33","doi-asserted-by":"crossref","first-page":"349","DOI":"10.3201\/eid2302.161012","article-title":"Outbreak of Legionnaire\u2019s Disease Caused by Legionella pneumophila Serogroups 1 and 13","volume":"23","author":"Kuroki","year":"2017","journal-title":"Emerg. Infect. Dis."},{"key":"ref_34","doi-asserted-by":"crossref","first-page":"e0051325","DOI":"10.1128\/spectrum.00513-25","article-title":"Comparative genome analysis investigation of nosocomial and community-acquired cases of Legionnaires\u2019 disease caused by ST2858 and ST378","volume":"13","author":"Najeeb","year":"2025","journal-title":"Microbiol. Spectr."},{"key":"ref_35","doi-asserted-by":"crossref","first-page":"1795","DOI":"10.3201\/eid2011.131872","article-title":"Legionnaires\u2019 disease incidence and risk factors, New York, New York, USA, 2002\u20132011","volume":"20","author":"Farnham","year":"2014","journal-title":"Emerg. Infect. Dis."},{"key":"ref_36","doi-asserted-by":"crossref","first-page":"107786","DOI":"10.1016\/j.ijid.2025.107786","article-title":"Occurrence of macrolides resistance in Legionella pneumophila ST188: Results of the Belgian epidemiology and resistome investigation of clinical isolates","volume":"153","author":"Michel","year":"2025","journal-title":"Int. J. Infect. Dis."},{"key":"ref_37","doi-asserted-by":"crossref","first-page":"95","DOI":"10.1128\/CMR.00029-14","article-title":"Current and emerging Legionella diagnostics for laboratory and outbreak investigations","volume":"28","author":"Mercante","year":"2015","journal-title":"Clin. Microbiol. Rev."},{"key":"ref_38","doi-asserted-by":"crossref","first-page":"623","DOI":"10.1038\/s41598-018-36924-w","article-title":"Legionella SBT applied directly to respiratory samples as a rapid molecular epidemiological tool","volume":"9","author":"Quero","year":"2019","journal-title":"Sci. Rep."},{"key":"ref_39","doi-asserted-by":"crossref","first-page":"603565","DOI":"10.2147\/IDR.S603565","article-title":"Legionellosis: Global Epidemiology and Current Perspectives on Diagnosis and Treatment","volume":"19","author":"Ma","year":"2026","journal-title":"Infect. Drug Resist."},{"key":"ref_40","unstructured":"British Columbia Centre for Disease Control (2023). Legionella Outbreak Investigation and Control Guidelines, British Columbia Centre for Disease Control."}],"container-title":["Infectious Disease Reports"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/2036-7449\/18\/5\/93\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2026,9,1]],"date-time":"2026-09-01T13:07:55Z","timestamp":1788268075000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/2036-7449\/18\/5\/93"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2026,8,26]]},"references-count":40,"journal-issue":{"issue":"5","published-online":{"date-parts":[[2026,10]]}},"alternative-id":["idr18050093"],"URL":"https:\/\/doi.org\/10.3390\/idr18050093","relation":{},"ISSN":["2036-7449"],"issn-type":[{"value":"2036-7449","type":"electronic"}],"subject":[],"published":{"date-parts":[[2026,8,26]]}}}